The present invention relates generally to automated spray painting or coating equipment and, in particular, to a novel cleaning system and method for a bell atomizer spray head.
In spray painting of various types of products, such as for example automobiles or automobile parts, automated machinery has been developed to spray a succession of parts in a continuous and rapid manner. Many applications use a variety of different types and colors of paint supplied to the same application devices (i.e. rotary atomizers and spray guns). In many of these applications, successive automobiles or parts therefore are to be painted a different color. In order to accomplish this color change, it is necessary to quickly clean and purge the paint supply lines leading to the applicators so as to avoid intermixing of the different colors. Often a single color paint is applied, such as a clear coat applied over the color base coat, and also requires periodic cleaning to remove any undesirable accumulation of paint.
Typical rotary atomizing coating devices have bell cups over which the paint flows and which are rotated at high speeds normally between 10,000 and 70,000 rpm. The electrostatically charged paint is fed to an inner chamber of the rotating bell cup where it is centrifuged forwardly through chamber openings to the larger diameter outer edge of the cup and is broken up into atomized particles as it escapes the bell cup edge. The axial centerline of the rotating bell cup is directed toward an electrically grounded workpiece which is to be coated. Because the atomized particles are centrifuged in a direction perpendicular to the axial centerline of the bell cup, it is known in prior art devices to redirect these particles so that they move toward the workpiece. In some situations, the electrostatic charge held by the atomized coating particles is sufficient to attract the particles to the grounded workpiece. It is also known in prior art rotary application devices to supply a cylindrically shaped curtain of shaping air which also directs the particles toward the workpiece. The shaping air is typically routed through passages within the atomizer housing and is supplied through a ring of holes or slots in a shaping air collar outboard of the bell cup. The shaping air also controls the diameter of the spray particle pattern.
During a color change, the interior and exterior of the bell cup, as well as the paint supply passages, must be cleaned and purged prior to introducing the next color into the system. Periodic cleaning of the bell cup is also required for single color paint systems to keep paint from drying on the cup. From the U.S. Pat. No. 5,072,881, a method is known to clean automated paint spraying equipment wherein an adjustable ratio mixing valve is utilized to intermix solvent and compressed air, which intermixed solvent and air is then routed through the manifolds and supply lines of the painting equipment.
Prior art methods for cleaning the atomizing bell cups consist typically of a single stream of a liquid only, typically a solvent, that is sprayed at the edge of the bell cup or introduced into a well in the back of the bell cup. These prior art methods also consume a higher amount of solvent when compared to using the above-mentioned solvent and air mixture. It is becoming increasingly necessary to use and expel a lesser amount of solvent, due to greater scrutiny and regulation by various governmental agencies. In addition, these prior art methods do not accomplish cleaning the shape air holes or cleaning of the face of the shaping air collar. It is also undesirable to have the front face cleaned manually because the paint can be inadvertently pushed into the shape air holes.
It is desirable to provide an apparatus and method to clean and purge the interior and exterior portions of the atomizing bell cup as well as the paint manifold when changing paint colors. It is also desirable to provide an apparatus and method to clean the shaping air holes and collar while reducing the amount of solvent required for the bell atomizer cleaning process. Furthermore, by cleaning the front face automatically, defects caused by dry particulate accumulating on the front face of the shape air ring are not expelled onto the part.
The present invention concerns a cleaning system and method for a bell atomizer spray head and fluid delivery system. A rotary atomizer spraying system includes a fluid manifold with a pump means, a compressed air supply, and a solvent supply attached thereto. An outlet of the pump means extends to a spray head having a shaping air manifold and shaping air passages included therein. The air and solvent supplies are connected to the paint manifold, the pump means and the spray head. During a color change sequence, the present invention injects a mixture of air and solvent into the shaping air manifold from which it proceeds to exit the shaping air holes and impact the exterior of the bell. In this way the shaping air manifold and passages, the shaping air holes, and the exterior of the bell cup are cleaned simultaneously. The solvent and air mixture can also be used to clean the injector and the insides of the bell cup. The shaping air passages are designed so that dead space is minimized, so the solvent and air remain a mixture, and so that liquid droplets cannot coalesce and later release in an undesirable point in the coating process. The solvent and air mixture significantly reduces the amount of solvent required for the cleaning process.
Alternatively, the solvent and air mixture can also be separately ported into a single or a plurality of holes independent of the shaping air system and used separately or in conjunction with the prior claims to clean the outside of the bell cup.
In addition, the present invention can be embodied advantageously in a handheld spray gun. The solvent and air mixture can be injected into the fan or shaping air ports of the spray gun.